According to PMBOK Guide, “The Schedule Performance Index (SPI) is a measure of schedule efficiency, expressed as the ratio of earned value to planned value.”
Schedule Performance Index (SPI) Formula –
The Schedule Performance Index(SPI) can be determined with the below formula.
Schedule Performance Index = (Earned Value) / (Planned Value)
SPI = EV / PV
So what do you interpret with the value you get out of SPI ?
- if SPI > 1, means you are ahead of schedule. More work has been completed compared to what was planned.
- if SPI = 1, means you are on time. All the work that was planned was completed
- if SPI < 1, means you are behind the schedule. Less work has been completed compared to what was planned.
Sample questions for Schedule Performance Index (SPI)
1. 5 people are working on a construction project. The initial estimate was to finish the task in 20 days. But they could only complete 80% of the task in 20 days. The project manager brought in 2 more resources and set the new target in 30 days. The team was able to complete the task in 25 days itself. What do you conclude on the schedule performance index of the project before and after the 2 people joined the team?
- Before the new team was formed the SPI was > 1. After 2 people joined SPI became < 1
- Before the new team was formed the SPI was > 1. After 2 people joined SPI was still > 1
- Before the new team was formed the SPI was < 1. After 2 people joined SPI was still < 1
- Before the new team was formed the SPI was < 1. After 2 people joined SPI became > 1
Correct Answer – Option D. The SPI was < 1 because 80% work was completed in 20 days. The SPI was 80/100 = 0.8. But after 2 new members joined the estimate was to complete by 30 days however the team completed the task in 25 days. So they are well ahead of the schedule, which means the SPI should be > 1.
2. A company was building ships for a private organization. The project was supposed to complete in 12 months. However, only 60% of the work got completed in 10 months due to delay in supply of raw materials from one of its vendors. In order to bring back the schedule on track, what should they do?
A. Make a note in the Risk register and explain the situation to the stakeholders
B. Seek options like fast tracking or crashing to bring back the schedule on track
C. Change the vendor who can supply raw materials on time to bring back the schedule on track
D. Schedule a meeting with current vendor to set the right expectations for quick delivery of raw materials
Correct Answer – Option B. Although it might sound other options reasonable, focus on the question. It asks how do you bring the schedule back on track. Since more than 60% of the work is completed, in order to bring back the schedule on track, you need to look for crashing or fast tracking so that by adding more resources you still meet the estimated timeline.